Corn, climate, and nitrogen

Every corn grower knows how important nitrogen is to grow corn and maintain yields. It’s a constant battle against nitrogen loss - with a lot of focus on nitrogen washing out into waterways. Reactive nitrogen can also be lost into the atmosphere, where it becomes a powerful greenhouse gas, nitrous oxide (N₂O), or as ammonia (NH₃), which can play a role in air pollution and impacts human health. In order to implement effective management strategies to mitigate emissions, researchers first need to be able to measure and understand them. 

Soil, Water, and Climate Professor Timothy Griffis and his lab have been working to better measure and understand nitrogen hotspots and moments in the corn belt. Using multiple tools, including field based measurements, tall towers, and even airplanes fitted with sensors, he and his team are looking to find not only where nitrogen emissions are coming from, but how the climate interacts with agricultural systems and impacts nitrogen loss. 

It’s a project Griffis started working on right away when he arrived on campus in 2002. He’s long been interested in nitrous oxide because it is 300 times more potent than carbon dioxide as a greenhouse gas. It is also one of the most important gases contributing to stratospheric ozone depletion. By looking at how agricultural systems and the atmosphere interact, researchers can track how much nitrogen is taken up by plants and how much is released. The goal is always to increase how much the plants benefit from the nitrogen and reduce how much is emitted into the atmosphere. 

The team is learning a lot depends on the climate — and how it is changing. 

“We’ve identified that warmer and wetter springs can enhance N₂O emissions. We’re concerned that a warmer and wetter climate will reduce nitrogen use efficiency,”Griffis says. “We are very interested in identifying hot moments so that we can develop better mitigation strategies. For example, our long-term measurements have identified that spring thaw results in very large N₂O emissions, which can account for over 30% of the annual budget.” Warmer and wetter years seem to be leading to more nitrogen emissions, which could lead to a feedback loop. N₂O emissions increase global warming, global warming leads to warmer and wetter years in Minnesota, leading to more nitrogen emissions. 

New research from the team also shows a substantial amount of N₂O emissions are a result of indirect processes and emitted offsite, like when nitrogen fertilizer drains from fields into the watersheds. Those watersheds, with an excess of nitrogen, then become hot spots for N₂O emissions.

With long term benchmark measurements in place, the team hopes to use the information to evaluate potential mitigation strategies to see what actually helps to reduce emissions in a warmer and wetter climate. 

“We’re comparing alternative management practices, like living mulch, to conventional cropping systems to see if they impact emissions,” Griffis explains. “We really want to know what the impact is before we recommend specific strategies on the basis of emissions. We want to make sure we provide the best science possible.” 

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